U.S. Pat. No. 2,278,473 to Musher, issued Apr. 7, 1941, discloses a process for subjecting green or roasted coffee to pressures of from about 20 to about 450 psi, at temperatures of from about 250.degree. to about 700.degree. F. (from about 121.degree. to about 371.degree. C.) for a period of time ranging from about 5 seconds to about 10 minutes. The pressure is then instantaneously released to make the coffee more porous for subsequent treatment or impregnation with air, moisture, steam, various solvents or various flavoring materials. The porous nature of the treated bean is also said toe enable heat to enter more quickly and uniformly during subsequent roasting.
U.S. Pat. No. 3,983,002 to Ohya et al, issued Sept. 28, 1976, discloses that hemicellulase (a cell-wall digesting enzyme), when incorporated into roast coffee beans, increases their extractability.
U.S. Pat. No. 3,644,122 to Yeransian, issued Feb. 22, 1972, discloses the treatment of ground roasted coffee with alkaline materials, e.g. ammonia, prior to extraction to provide a darker colored coffee product having increased yield of soluble solids.